"Despite what we have said over the last 10 years, pregnant women are still afraid exercise is going to hurt their child," says researcher Melissa J. Hague, MD, a clinical assistant professor of obstetrics and gynecology at the University of Kansas School of Medicine in Wichita.

In her study of 90 women, she found many regular exercisers stopped working out when they became pregnant. Some told her they did not think exercising, even walking, was safe during pregnancy.

"I was really surprised," she tells WebMD.

Hague presented her findings this week at the annual meeting of the American College of Obstetricians and Gynecologists (ACOG) in San Diego.

Exercise During Pregnancy: Expert Opinion

In 2002, ACOG issued an opinion about exercise during pregnancy. Recreational and competitive athletes without pregnancy complications can remain active with their doctor's OK, it says. They should modify their workouts as medically indicated.

Inactive women should consult their doctors before starting a program, it says.

Moderate exercise for 30 minutes or more most or all days of the week appears safe for pregnant women without complications, it says. Activities with a high risk of falling, contact sports, and scuba diving should not be done.

Exercise During Pregnancy: Study Details

Hague cares for pregnant women in her practice. She was curious as to why so many do not exercise.

She and her team did phone interviews with 90 women. They were 16 to 30 weeks pregnant.

Before becoming pregnant, almost half of the women said they exercised moderately at least 90 minutes a week.

After becoming pregnant, less than 27% did. "They said they were afraid they were going to hurt the baby," Hague says.

Safety concerns were more of an issue with those who weren't active, Hague found.

About 62% of those who exercised during pregnancy thought working out longer than 30 minutes is safe.

Nearly 89% of white women said brisk walking is safe during pregnancy, and 90% said swimming is safe.

Only 60% of other ethnic groups thought brisk walking is safe, and only 67% thought swimming is.

Myths passed down within the family may trigger women's fears, Hague tells WebMD. "If the moms tell them, 'You are going to hurt the baby,' they are not going to do it," she says of exercise during pregnancy.

Certain women were more likely to exercise during pregnancy, including those who believed they could manage it despite a busy schedule. Those who worked outside the home were more likely to fit in exercise during pregnancy.

Exercise During Pregnancy: Perspective

The study findings may reflect Midwest attitudes, says Raul Artal, MD, chair and professor of obstetrics, gynecology, and women's health at St. Louis University School of Medicine, and an expert on exercise during pregnancy.

He reviewed the study findings.

"The Midwest is experiencing an epidemic of obesity," he says. "If the study were done in Colorado, New York, or L.A., there may be different findings," he tells WebMD.

Doctors must take part of the blame for women not getting the exercise message, he says. "Physicians as a whole don't receive a lot of education about exercise physiology and behavior modification. This includes exercise and diet."

"There is still much ignorance about the fact that pregnancy should not be a state of confinement," Artal says.

Pregnancy, he says, "is a good time to engage in a healthy lifestyle," including exercise, with certain exceptions such as scuba diving, which can put the fetus at risk for decompression sickness.

"For women who have never exercised, walking is a good way to start" after getting a doctor's OK, Artal tell WebMD.

Hague says women should focus on the benefits of exercise during pregnancy. "We know exercise has significant benefits for women, including reducing their risk of depression and their risk of excess weight gain," she says. "Minimizing excess weight gain can reduce the risk of C-section."

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

SOURCES:American College of Obstetricians and Gynecologists annual clinical meeting, May 5-9, 2012, San Diego.Melissa J. Hague, MD, clinical assistant professor of obstetrics and gynecology, University of Kansas School of Medicine, Wichita.Raul Artal, MD, chair and professor of obstetrics, gynecology and women's health, St. Louis University School of Medicine.American Congress of Obstetricians and Gynecologists' Committee Opinion: "Exercise During Pregnancy and the Postpartum Period."